The invention relates to an apparatus for the controlled ventilation of rooms, with a control member incorporated into a duct portion for constricting the flow cross-section in the duct portion, with a control drive for the control movement of the control member of a measuring device for measuring the flow quantity through the duct portion and with a controller located between the measuring device and the control drive and connected thereto, the measuring device having two measurement points succeeding one another in the flow direction for measuring a pressure difference decisive for the quantity measurement.
An apparatus of the aforementioned type positioned at a not defined point in a flow duct is e.g. known from EP-A-0 128 690. The production of the Venturi-type, constricted duct portion is complicated because the latter, like the complete duct wall for ventilation systems, must be made from heat-resistant material for safety reasons.
The problem of the invention is to provide an apparatus of the aforementioned type, which as a result of a favourable, uniform flow guidance permits a particularly accurate measurement and control, leads to low flow losses and which is constituted by a few, easily manufacturable parts. It preferably has a short size in the flow direction, so that it can in particular be incorporated into a ventilating system adjacent to the branch of a main duct or areas having a non-uniform flow.